This invention relates to yarn delivery systems, and in particular to a delivery system for the delivery of precise lengths of yarn from a yarn supply to a yarn utilising point at a rate required by that utilising point.
It is known in relation to various yarn processes to store a length of yarn in a storage device or accumulator disposed between a yarn supply and a yarn processing station or utilisation point. Such devices generally comprise a chamber into which the yarn is fed, generally by compressed air, and from which the yarn is withdrawn by the yarn processing or utilising devices. Within the chamber the yarn may accumulate in a succession of folds or layers. For many applications such arrangements may well be satisfactory. However, in the case of supplying yarn to a knitting machine, a primary aim in producing a high quality knitted product, i.e. as regards dimensions, pressure characteristics, stiffness and shape retention, is that of defined stitch length throughout the knitted fabric. Heretofore, yarn has been withdrawn from the supply or from the store by the knitting needles as required, but the problem of ensuring precision stitch length control has not been solved wholly satisfactorily in either case. This problem is particularly acute in the cases of fabrics knitted on flat-bed knitting machines and in the use of elastomeric yarns, which can extend by over 600%. Furthermore accumulation of fine, high modulus or elastomeric knitting yarn in layers or folds can lead to twisting or snarling of the yarn, which provides that the feed to the knitting machine is unsatisfactory or even breaks down.
It is an object of the present invention to provide a yarn delivery system from a yarn supply to a yarn utilising point at a precise rate required by that utilising point, which does not have the abovementioned disadvantages of known storage or accumulator devices. It is also an object of the invention to provide a yarn delivery system capable of delivering precise lengths of yarns such as elastomeric yarns, particularly to flat bed knitting machines.
The invention provides a precision yarn delivery system for the delivery of yarn from a yarn supply to a yarn utilising point, comprising a temporary yarn store intermediate the supply and the utilisation point in which the yarn is held under low tension and is fed from the store as required by the utilisation point.
The yarn in the store may allowed to relax at a tension less than that at which it is withdrawn from the supply, and may be held under a uniform substantially zero tension. The system may comprise a chamber in which the yarn is stored, and the yarn may be stored in the chamber under pneumatic control. The pneumatic control may be provided by suction applied to the chamber. The chamber may comprise an elongate tube, which may have a width to prevent twisting of the yarn therein. A yarn inlet to and a yarn outlet from the chamber may be at one end of the chamber, and the yarn may be constrained to form a single loop in the chamber. The suction may be applied to the chamber at the other end thereof.
The system may comprise an output feed device, which may be disposed spaced from the yarn outlet from the chamber. The output feed device may comprise a pair of feed rollers. The system may also comprise an input feed device, which may be disposed adjacent the yarn inlet to the chamber. The input feed device may comprise a pair of feed rollers. The input feed device and the output feed device may be driven by a common drive arrangement, and the input feed device may be driven at a higher speed than the output feed device. The drive arrangement may comprise gearing operable to determine the ratio of the speed of the input feed device to that of the output feed device. The gearing may be selectable dependent on the elasticity of the yarn to be stored. A motor may be disposed to drive the gearing, and the motor may be a precision servo motor or a stepper motor.
The invention also provides a knitting machine having a precision yarn delivery system for the delivery of yarn from a yarn supply to a knitting point, comprising a temporary yarn store intermediate the supply and the knitting point in which the yarn is held under low tension and fed from the store as required by the knitting point. The knitting machine may be a flat bed knitting machine.
The knitting machine may comprise a carriage operable to engage a selected carrier and to move the carrier along a rail of the machine in accordance with a signal from a control arrangement. The carrier may have the precision yarn delivery system mounted thereon. The carriage may have a motor and a coupler mounted thereon. The coupler may be operable to engage a shaft of the motor with gearing of the precision yarn delivery system when the carriage is engaged with the carrier. The coupler may be operated by means of electro pneumatic cylinders or by solenoids. Suction may be applied to the store whilst the carriage is in engagement with the carrier.
The system may comprise two stores and respective input feed devices, whereby two yarns may be fed to the knitting point.